The present invention relates to manufacturing methods for two-dimensional image detectors capable of detecting images by means of X-rays and other kind of radiation and visible, infrared, and other kind of light and also relates to those two-dimensional image detectors.
Conventionally known radiation two-dimensional image detectors (hereinafter, will be referred to simply as two-dimensional image detectors) include semiconductor sensors arranged in rows and columns with a switching element provided to each of the sensors. The semiconductor sensor generates electric charges (electron-hole pairs) upon detection of X-rays or other radiation (hereinafter, will be simply referred to as radiation). In the two-dimensional image detector, all the switching elements in a row are turned on to read electric charges from the semiconductor sensor in each column. The reading operation is performed for each column to detect a two-dimensional image.
The structure and principles of the two-dimensional image detector are explained in specific terms in publications including L. S. Jeromin, et al., xe2x80x9cApplication of a-Si Active-Matrix Technology in a X-Ray Detector Panelxe2x80x9d, SID 97 DIGEST, pp. 91-94, 1997; and Japanese Laid-Open Patent Application No. 6-342098/1994 (Tokukaihei 6-342098; published on Dec. 13, 1994).
Now, the structure and principles of the conventional two-dimensional image detector will be discussed in reference to FIGS. 17 and 18. Whilst FIG. 17 is a perspective view schematically showing a structure of the two-dimensional image detector, FIG. 18 is a cross-sectional view showing a structure of a pixel shown in FIG. 17.
The two-dimensional image detector includes an active matrix substrate 100, a photoconductive film 112, a dielectric layer 114, an upper electrode 116, a high voltage source 118, and an amplifier 120.
The active matrix substrate 100 is constituted by a glass substrate 102, electrode wires (gate electrode line 104a and data electrode line 104b) 104 arranged in an XY matrix (arranged in rows and columns) on the glass substrate 102, thin film transistors (hereinafter, will be referred to as TFTs) 106 connected to the electrode wires 104, electric charge storage capacitances 108 connected to the TFTs 106, etc.
The active matrix substrate 100 may be one of those used in manufacture of liquid crystal displays. An active matrix substrate used in an active matrix liquid crystal display (AMLCD) includes, among other components, TFTs 106 formed from amorphous silicon (a-Si) or polysilicon (p-Si), electrode wires 104, and electric charge storage capacitances 108, and can be used in the two-dimensional image detector with few modifications in design.
The photoconductive film 112, the dielectric layer 114, and the upper electrode 116 are formed so as to cover a substantial entirety of the active matrix substrate 100.
The photoconductive film 112 is composed of a semiconductor material that produces electric charges (electrons-holes) when exposed to radiation. In the documents cited above, amorphous selenium (hereinafter, will be referred to as a-Se) is employed for use as the photoconductive film 112, since the material has high dark resistance, exhibits satisfactory photoelectricity when exposed to radiation (X-rays), and is easy to form large films by vapor deposition. Specifically, a-Se is deposited 300 xcexcm to 600 xcexcm thick by vacuum vapor deposition to form the photoconductive film 112.
Now, the operation principles of the two-dimensional image detector will be discussed.
When the photoconductive film 112 composed of a-Se is exposed to radiation, electric charges (electrons-holes) develop in the photoconductive film 112. As shown in FIGS. 17 and 18, the upper electrode 116 is electrically connected in series with Cs electrodes 108a in the electric charge storage capacitances 108. Upon application of voltage across the upper electrode 116 and the Cs electrodes 108a, those electrons and holes developing in the photoconductive film 112 move toward the anodes and cathodes, building up electric charges in the electric charge storage capacitances 108.
The electric charges thus accumulated in the electric charge storage capacitance 108 are sent to the amplifier 120 through the data electrode line 104b by changing the TFT 106 into an on-state by means of an input signal from the gate electrode line 104a. Since the electrode wires 104 (the gate electrode lines 104a and the data electrode lines 104b), the TFTs 106, and the electric charge storage capacitances 108 are arranged to form an XY matrix as explained earlier, information on a two-dimensional radiation image is obtainable by sending an input signal sequentially to the gate electrode lines 104a. 
If the photoconductive film 112 exhibits photoconductivity to visible or infrared light as well as in radiation, the two-dimensional image detector can function as a two-dimensional visible or infrared image detector. For example, an a-Se film mentioned above exhibits a satisfactory level of photoconductivity to visible light and avalanche effect on the application of a strong electric field. Studies are under way to develop supersensitive image sensors (two-dimensional image detectors) by means of the avalanche effect.
In manufacture of the two-dimensional image detector, the three processes A to C below are indispensable following the fabrication of active matrix elements (including the TFTs 106 and the electric charge storage capacitances 108).
A. A-Se Film Deposition Process
In this process, an a-Se film is deposited by means of vacuum vapor deposition on the active matrix substrate 100 so as to cover at least areas in which the active matrix elements are formed.
B. Glass Cutting Process
In this process, a piece of mother glass is cut into the active matrix substrate 100 by a scribe or dicing technology.
Here, mother glass refers to the base material of the piece of glass on which active matrix elements are fabricated. Dividing a piece of mother glass into a designated dimensions will form active matrix substrates 100.
Further, in this process, after active matrix substrates 100 are cut out, the edges along which the active matrix substrate 100 has been cut out are subjected to a chamfering process as necessary.
The glass cutting process is performed after the fabrication of matrix elements for the following reasons. First, the production line for active matrix substrates 100 includes dedicated machines exclusively used for a particular substrate size. Accordingly, the piece of mother glass, after having been subjected to the process to fabricate active matrix elements, needs to be of a size suitable to those dedicated machines. The piece of mother glass thus processed is then divided into smaller pieces of a required size for use as two-dimensional image detectors.
The second reason is that it is difficult in the fabrication process of active matrix elements to fabricate normal active matrix elements near the periphery of a glass substrate. This is chiefly due to the difficulty to satisfy suitable conditions for the fabrication of active matrix elements near the periphery of a glass substrate and the handling assembly directly contacting the periphery of the glass substrate. Therefore, the piece of mother glass needs to be of a size that actually forms the two-dimensional image detectors, plus the periphery. The unnecessary periphery is cut off after the fabrication of active matrix elements.
C. Mounting Process
In this process, various components and circuitry are mounted on the active matrix substrate 100 so as to obtain electric charges and other information from the active matrix substrate 100.
However, regarding a two-dimensional image detector with an a-Se film deposited covering a substantial entirety of the active matrix substrate 100, the following problems occur in its manufacturing process.
It is known that if pollutants in water, air, and the like stick to a typical a-Se film after its deposition, it is likely to change its properties, e.g., crystalize, starting where those foreign objects stick.
Therefore, if an a-Se film deposition process is followed by a glass cutting process and a mounting process, foreign objects, such as glass particles formed during the cutting process, processing water used for dicing and chamfering, and dust developing during the mounting process, touch the a-Se film and causes deterioration of properties of the a-Se film.
Meanwhile, if a glass cutting process and a mounting process are followed by an a-Se film deposition process, the surface of the active matrix substrates 100 is polluted with the glass particles, processing water, and dust.
Especially, glass particles are hazardous in its possibility of scratching the active matrix elements. They are even so, if they are small and stick to the surface of the active matrix substrate 100, because it is very difficult to remove them with supersonic wave or another similar cleaning technique. In addition, the TFTs 106, forming part of the active matrix element, are very sensitive to pollution. If an a-Se film is deposited on a polluted active matrix element, the a-Se film also becomes polluted, which causes deterioration of properties in both the a-Se film and the active matrix element.
Even after the two-dimensional image detector is completely manufactured, dew drops may develop inside the two-dimensional image detector depending on the environment, causing deterioration in properties of the a-Se film.
In the two-dimensional image detector, an electric field approximately as high as 10V/xcexcm needs to be applied to the photoconductive film 112 to improve the efficiency in collecting electric charges. For this purpose, a voltage from couple of thousands to ten thousands volts is applied to the upper electrode 116. Therefore, electric discharge is likely in the vicinity of the upper electrode 116, destructing elements or deteriorating their properties.
The present invention has an object to prevent deterioration in performance of the a-Se film (semiconductor layer) and the active matrix substrate. For this purpose, methods of manufacturing a two-dimensional image detector are presented whereby the a-Se film and the active matrix substrate are not polluted in the manufacturing process. Also, arrangements of two-dimensional image detectors are presented that can resolve problems in use environment, typically represented by dew drops and electric discharge in the two-dimensional image detector, and that offers a satisfactory level of insusceptibility to environmental conditions.
To achieve the object, a method of manufacturing a two-dimensional image detector in accordance with the present invention is a method of manufacturing a two-dimensional image detector including:
a semiconductor layer for producing electric charges according to incident electromagnetic waves; and
a substrate having an active element array for reading out the electric charges produced by the semiconductor layer,
the manufacturing method comprising the steps of:
(1) forming the active element array on the substrate;
(2) forming a protection member on the substrate so as to cover an area in which the active element array is formed;
(3) dividing into smaller pieces the substrate on which the protection member is already formed;
(4) removing the protection member from the divided pieces; and
(5) forming the semiconductor layer on the active element array where the protection member is removed.
According to the method, an active element array is formed on a substrate, and then a protection member is formed on the active element array. Subsequently, the substrate is divided. After removing the protection member, a semiconductor layer is formed on a surface of the active element array which was protected by the protection member.
As mentioned above, depending on the production line to fabricate substrates (active matrix substrates) with an active element array, sometimes it becomes necessary to divide the substrate into active matrix substrates of a preferred size after the formation of the active element array on the substrate. When the substrate is divided, the substrate comes in contact with materials that can scratch or pollute the active element array (hereinafter, will be collectively referred to as pollutants), such as glass particles and processing water. The same phenomenon happens when the substrate is divided and the divisions are chamfered.
By contrast, in the method, the active element array is covered with a protection member when the substrate is divided. This prevents pollutants produced in the division of the substrate from directly contacting the active element array.
As a result, the active element array can be kept clean and free from scratches, and the deterioration in performance of the active element array can be prevented. As a result, according to the method, active matrix substrates are manufactured with the active element array operating reliably and stably. In addition, the production yields of the active matrix substrates improve.
Besides, the semiconductor layer for converting electromagnetic waves information into electric charges information can be formed on the surface of the active element array that is clean because being exposed by removing the protection member only after dividing the substrate. Therefore, the semiconductor layer can be prevented from contacting pollutants produced in the division of the substrate. Thus, according to the method, the semiconductor layer can be prevented from deteriorating in terms of performance and reliability improves, even when the semiconductor layer is constituted by an a-Se film or other materials that are highly sensitive to pollutants.
As a result, highly reliable two-dimensional image detector can be manufactured with the active element array and the semiconductor layer exhibiting a satisfactory level of performance.
Another method of manufacturing a two-dimensional image detector in accordance with the present invention is a method of manufacturing a two-dimensional image detector including:
a semiconductor layer for producing electric charges according to incident electromagnetic waves; and
a substrate having an active element array for reading out the electric charges produced by the semiconductor layer,
the manufacturing method preferably comprising the steps of:
(1) forming the active element array on the substrate;
(2) forming the semiconductor layer on the active element array;
(3) forming a protection member on the substrate so as to cover an area in which the semiconductor layer is formed; and
(4) dividing the substrate on which the protection member is already formed.
According to the method, an active element array formed on a substrate, and topped by a semiconductor layer. Then a protection member is formed to cover an area in which the semiconductor layer formed, followed by the division of the substrate.
In the method, the semiconductor layer can be formed on the active element array after the step of forming the active element array, but before any step that produces pollutants.
Therefore, the active element array can be prevented from pollution, and the semiconductor layer can be formed on a clean surface.
Further, according to the method, the substrate is divided with the protection member being provided to cover the area in which the semiconductor layer is formed; therefore, the semiconductor layer can be prevented from being polluted by the aforementioned pollutants during the division of the substrate.
Furthermore, in the method, the step of removing the protection member can be omitted. This reduces the number of steps required in manufacture and leaves the protection member unremoved, providing protection to the semiconductor layer during a later step of mounting circuit components and even after the completion of the two-dimensional image detector. This provides substantially perpetual protection to the semiconductor layer until the two-dimensional image detector is delivered as a finished product.
As a result, two-dimensional image detector having lasting high reliability can be manufactured with the active element array and the semiconductor layer exhibiting a satisfactory level of performance.
Another method of manufacturing a two-dimensional image detector in accordance with the present invention is a method of manufacturing a two-dimensional image detector including:
a semiconductor layer for producing electric charges according to incident electromagnetic waves; and
a substrate having an active element array for reading out the electric charges produced by the semiconductor layer,
the manufacturing method comprising the steps of:
(1) forming the active element array on the substrate;
(2) forming the semiconductor layer so as to cover the active element array;
(3) forming on the semiconductor layer a surface electrode layer through which a bias voltage is applied to the semiconductor layer;
(4) forming a protection member on the substrate so as to cover the semiconductor layer and the surface electrode layer; and
(5) dividing into smaller pieces the substrate on which the protection member is already formed.
According to the method, an active element array is formed on a substrate, and topped sequentially by a semiconductor layer and a surface electrode layer. Then a protection member is formed on the substrate so as to cover the semiconductor layer and the surface electrode layer. Thereafter, the substrate is divided with the protection member being provided thereon.
Thus, a protection member is formed on the substrate to cover the semiconductor layer and the surface electrode layer, and only subsequently the substrate is divided; therefore, glass particles and processing water produced or used during the division do not directly pollute the semiconductor layer and the surface electrode layer. In other words, the protection member ensures that the semiconductor layer and the surface electrode layer are protected from pollution with glass particles and processing water. Further, the active element array is covered with a semiconductor layer protected by the protection member; therefore, the active element array per se is not polluted by glass particles and processing water.
As a result, the active element array, the semiconductor layer, and the surface electrode layer can be kept clean and free from scratches, and the deterioration in performance of the active element array, the semiconductor layer, and the surface electrode layer can be prevented. As a result, according to the method, highly reliable active matrix substrates are manufactured with the active element array operating stably and the semiconductor layer and the surface electrode layer exhibiting a lasting satisfactory level of performance. So are two-dimensional image detectors. In addition, the production yields of the active matrix substrates improve.
A two-dimensional image detector in accordance with the present invention includes:
a substrate;
an active element array provided on the substrate;
a semiconductor layer, provided on the active element array, for producing electric charges according to incident electromagnetic waves so that the electric charges are read out by the active element array; and
a protection member, provided on the substrate, for covering the semiconductor layer.
According to the arrangement, a protection member is provided to cover the semiconductor layer on the active element array; therefore, pollutants produced in the use of the two-dimensional image detector can be prevented from directly contacting the active element array and the semiconductor layer. Since the protection member is disposed on the substrate, a minimum area including the active element array and the semiconductor layer can be protected. Therefore, when the two-dimensional image detector is disassembled thoroughly into components for maintenance for example, the active element array and the semiconductor layer are still protected from pollutants.
As a result, highly reliable two-dimensional image detectors can be manufactured with the deterioration in performance of the active element array and the semiconductor layer being effectively prevented even after the manufacturing process.
Further, by providing the protection member so as to cover the semiconductor layer, electric discharge can be prevented from happening around the semiconductor layer even when a high voltage is applied to the semiconductor layer. This protects components from destruction due to electric discharge, as well as prevents the aforementioned pollution and deterioration in performance of the active matrix element and the semiconductor layer. Furthermore, the protection member isolates the semiconductor layer from ambient air, preventing dew drops from developing in, and thus degrading the properties of, the semiconductor layer.
Another two-dimensional image detector in accordance with the present invention includes:
a substrate;
an active element array provided on the substrate;
a semiconductor layer, provided on the active element array, for producing electric charges according to incident electromagnetic waves so that the electric charges are read out by the active element array;
a surface electrode layer, provided on the semiconductor layer, for allowing a bias voltage to be applied to the semiconductor layer; and
a protection member, provided on the substrate, for covering the semiconductor layer and the surface electrode layer.
According to the arrangement, a protection member is provided to cover the semiconductor layer and the surface electrode layer on the active element array; therefore, pollutants produced in the use of the two-dimensional image detector can be prevented from directly contacting the active element array, the semiconductor layer, and the surface electrode layer.
Since the protection member is disposed on the substrate, a minimum area including the active element array, the semiconductor layer, and the surface electrode layer can be protected. Therefore, when the two-dimensional image detector is disassembled thoroughly into components for maintenance for example, the active element array, the semiconductor layer, and the surface electrode layer are still protected from pollutants.
As a result, highly reliable two-dimensional image detectors can be manufactured with the deterioration in performance of the active element array, the semiconductor layer, and the surface electrode layer being effectively prevented even after the manufacturing process.
Further, by providing the protection member so as to cover the semiconductor layer and the surface electrode layer, electric discharge can be prevented from happening around the semiconductor layer and the surface electrode layer even when a high voltage is applied to the semiconductor layer via the surface electrode layer. This protects components from destruction due to electric discharge, as well as prevents the aforementioned pollution and deterioration in performance of the active matrix element, the semiconductor layer, and the surface electrode layer. Furthermore, the protection member isolates the semiconductor layer and the surface electrode layer from ambient air, preventing dew flops from developing in, and thus degrading the properties of, the semiconductor layer and the surface electrode layer.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.